1. Field of the invention
The present invention relates to a rack bar supporting device of a steering apparatus for a vehicle. More particularly, the present invention relates to a rack bar supporting device of a rack and pinion type steering apparatus for a vehicle, which can prevent free movement from increasing by automatically adjusting a predetermined free movement even when wear occurs in a support yoke after degradation of driving durability of the vehicle, and can prevent a noise from occurring caused by an increase of free movement when the support yoke collides with a yoke plug by an impact reversely input from an uneven road surface, etc.
2. Description of the Prior Art
In general, a steering apparatus is an apparatus which allows a driver to freely change an advancing direction of a vehicle. In other words, the apparatus is an assist apparatus which allows a driver to freely change a rotation center of turning of a front wheel of the vehicle and to advance the vehicle in a required direction.
FIG. 1 is a schematic configuration view illustrating a conventional rack and pinion type steering apparatus.
As shown, the conventional rack and pinion type steering apparatus includes: a steering wheel 100 disposed in a driver's seat; a steering shaft 105 connected to the steering wheel 100; a steering column 103 configured to fix the steering shaft to a vehicle body; a gear box 130 including a rack gear 110 and a pinion gear 120 which convert a rotation force received from the steering shaft 105 into a linear motion; a rack bar 140 provided with inner ball joints 135 at both ends thereof, and a tie rod 150 integratedly formed with a ball of each of the inner ball joints 135.
Also, the tie rod 150 is connected to an outer ball joint 155 and transfers a force to a knuckle 159, so as to steer a tire 158.
FIG. 2 is a cross-sectional view illustrating a conventional rack bar supporting device.
As shown, the conventional rack bar supporting device includes a pinion gear 120, a rack bar 140, a support yoke 260, a spring 263, and a yoke plug 265. A rack and pinion type gear box 130, as described above, converts a rotation force received from a steering shaft (not shown) into a linear motion.
The rack bar 140 converts a rotary motion into a linear motion by meshing with the pinion gear 120. At the rear surface of the rack bar 140, a device for supporting the rack bar 140 toward the pinion gear 120 is provided so as to facilitate the mesh of the rack bar 140 and the pinion gear 120.
The device for the rack bar 140 includes the support yoke 260, the spring 263, and the yoke plug 265. The support yoke 260 is positioned at the opposite side to the formation surface of the rack gear 110 (see FIG. 1) as the rear surface of the rack bar 140, and has a structure in which it can move in front/rear directions perpendicular to the rack bar 140 by being inserted in a cylinder 250 of the gear box 130.
The support yoke 260 has a cylindrical shape so that it can slide in the front/rear directions within the cylinder 250. Also, at the support yoke 260's front side contacting with the rack bar 140, a semicircular groove is formed so as to closely contact with the rear surface of the rack bar 140.
Also, at the rear side of the support yoke 260, the spring 263 is disposed so that the rack bar 140 and the pinion gear 120 can closely contact with each other and effectively transfer a force. The spring 263 pushes the support yoke 260 at a predetermined pressure so as to compensate free-movement occurring between the rack bar 140 and the pinion gear 120.
The support yoke 260 as described above slidingly rubs against the rear surface of the rack bar 140. Thus, in order to prevent the rack bar 140 from being worn or a noise from occurring by friction, the support yoke 260 is made of a plastic material softer than the conventional rack bar 140.
The spring 263 received in a spring groove 220 has a function of pressing the support yoke 260 in such a manner that the support yoke 260 can closely contact with the rack bar 140. In general, as the spring 263, a coil spring is used. At the rear surface of the spring 263, the yoke plug 265 is positioned so as to support the spring 263.
The yoke plug 265 supports the spring 263 in such a manner that the spring 263 can press the support yoke 260. In the yoke plug 265, in general, a screw thread and a screw groove are formed so that they can couple with the gear box 130 and a lock nut 240, the gear box 130 and the lock nut 240 being formed with another screw thread and another screw groove to mesh with them. At the rear surface of the yoke plug 265, a tool groove 230 into which a wrench can be inserted is formed.
However, the conventional rack bar supporting device as described above has a problem in that due to high friction, as the support yoke is worn to some extent, it cannot sufficiently support the rack bar by an increase of free movement. Furthermore, there is a problem in that due to the increase of free movement, a rattle noise occurs in the support yoke and the yoke plug.
In the conventional rack bar supporting device as described above, there is a problem in that when the durability of the support yoke contacting with and supporting the rack bar is degraded to some extent, the rattle noise occurring by free movement due to wear and the insufficient supporting of the rack bar reduce the stability of steering.
Also, when free movement occurs by the wear of the support yoke, the displacement of the spring coupled to compensate free movement increases by the increased free movement. This reduces tension of the spring. Thus, there is a structural problem in that even though the same impulse is added, the noise is increased.